The principal goals of this work are threefold: (1) To study the guidance of axons along previously aneural epithelial tissue; (2) To extend an ongoing study of glia in mature insects back into embryonic stages, looking especially at the interaction of glial and neural cells in the overall construction of the nervous system; and (3) To examine the process of pathfinding by the first axons growing in a variety of regenerating appendages. In all these studies there is a strong focus on the interaction of nerve cells with other cell types, an issue that reaches freely across phyletic lines. (1) Epithelial-neural interactions will be studied in the developing wings of the fruitfly Drosophila, mainly by generating monoclonal antibodies whose binding distribution in the wing suggests a possible role in axon guidance. Extensive existing data concerning normal neurogenesis in the wing, the behavior of neurons isolated from their normal neighbors, and the growth of axons from cells grafted to geneticalliy aneural epithelia will make specific interpretations of the observed binding patterns testable. Antibodies will be screened, and basic results obtained, on whole-mounted specimens. Anatomical details will be studied by light and electron microscopy combined, when appropriate, with immunocytochemistry. (2) An immunological characterization of glial cells in the cricket Acheta will be directed to understanding their distribution and origin, and ultimately their function and role in development and regeneration. Monoclonal antibodies already prepared, and further ones to be made, will be used in whole-mounted embryos, frozen sections, and plastic-embedded and sectioned material for light and electron microscopy. (3) The origin and behavior of pioneer neurons in regenerating sensory appendages of Acheta and of the firebrat Thermobia will be studied mainly with the anti-HRP technique that reliability stains insect neurons. Factors that govern the choice of pathway within the regenerate and en route to the CNS will be studied. These three systems provide distinct technical advantages for the analysis of these conceptually related problems, as well as broadening the biological scope of the study. The problems are basic ones of cell-cell interaction in neurogenesis, and the results will also be of interest in the study of neural development in vertebrates. The studies on regeneration and the role of glia in this process are related to problems of great clinical importance.